To do so without Poland's agreement is almost inconceivable, our correspondent says.

Diplomats are being very cautious about the German proposal, described as quite premature by one, while others say the suggestion is designed simply to put pressure on Poland.

Various solutions have been offered to try to overcome Poland's objections to the new voting system.

As President Kaczynski continued tough talks in Brussels, his brother said the offer on the table, that would have delayed introducing a new voting system for seven more years, was "far too little to be acceptable".

Speaking live on Polish television, Jaroslaw Kaczynski said Poland was open to compromise but that "one cannot give way all the time".

Concessions

Earlier, the UK and others asked for clarification on why reference to the EU's commitment to free competition had been dropped from the draft treaty at the request of the French.

"The notion that this in any shape or form changes the legal basis of the internal market and the way the European economy works and the Commission's powers in relation to it is wrong," said Mr Blair, adding that a protocol would be added to the treaty.

EU leaders have struck other compromises, including the job title of a new EU foreign policy chief.

The post-holder will not be called a minister, as in the European Constitution, but High Representative of the EU, and will combine the job of the vice-president of the European Commission, which comes with a significant aid budget and staff.

A draft treaty submitted for debate at the summit makes several concessions to EU member states that had opposed key parts of the planned constitution.

Proposed changes include:

Removing any mention of the word "constitution"

Providing countries with a chance to opt out of EU policies in the area of policing and criminal law

New voting system to approve decisions

Full-time president of European Council instead of current system where members take six-month turns

New foreign affairs head and a smaller commission

Correspondents say failure to reach a deal on the treaty would plunge the EU into a fresh crisis as deep as the one that followed the rejection of the constitution two years ago.